1. Field of the Invention
The present invention relates to an electrophotographic image forming device such as a printer, copier, and facsimile machine. More particularly, the present invention relates to a tandem color image forming apparatus to transfer toner images formed respectively on a plurality of photosensitive bodies by a plurality of corresponding image forming units, onto an intermediate transfer unit or printing medium.
2. Description of the Related Art
A conventional electrophotographic tandem color image forming device is provided with a plurality of image forming units disposed in parallel, a plurality of photosensitive bodies, each being disposed in the corresponding image forming units and forming toner images representing yellow, magenta, cyan and black colors, respectively, and a transfer unit such as a transfer belt or a transfer drum to sequentially transfer the toner images formed on the photosensitive bodies onto a recording medium such as a sheet of printing paper. Additionally, conventional electrophotographic tandem color image forming devices include a fusing unit to fuse and fix the toner images transferred onto the recording medium with heat and pressure.
Other conventional tandem color image forming devices further include an intermediate transfer unit disposed between the photosensitive bodies and the transfer unit. In this case, the toner images formed on the photosensitive bodies are not directly transferred to the recording medium, but are first transferred as a first transfer image onto the intermediate transfer unit and then retransferred from the intermediate transfer unit onto the recording medium.
The conventional tandem color image forming devices that have the plurality of photosensitive bodies therein for forming images by simultaneously revolving the plurality of photosensitive bodies have an advantage in that they can obtain color images very quickly, as compared with other color image forming devices that have only a single photosensitive body therein for forming images by revolving the single photosensitive body several times. Since construction is complicated with use of a plurality of photosensitive bodies and image forming units, it is important that the tandem color image forming device be constructed to be easily assembled, maintained and repaired.
FIGS. 1 and 2 show a tandem image forming device having a mounting frame for easily assembling, maintaining, and repairing. The tandem image forming device is disclosed in Japanese patent No. 2002-108049, the entire contents of which are incorporated herein by reference.
The color image forming device 1 comprises a paper feeding unit 21 to feed sheets of printing paper P stacked in a paper cassette 20, four image forming units 10Y, 10M, 10C and 10K to form toner images of four colors, i.e., yellow, magenta, cyan, and black disposed vertically in parallel, and an intermediate transfer unit 7 having a belt-shaped intermediate transfer element 70 (FIG. 5) rotatably supported on a plurality of rollers 71, 72, 73 and 74 (FIG. 5) at a left side of photosensitive bodies 1Y, 1M, 1C, and 1K disposed respectively in the image forming units 10Y, 10M, 10C and 10K. The color imaging forming device 1 further comprises a mounting frame 8 to install the image forming units 10Y, 10M, 10C and 10K and the intermediate transfer unit 7 therein, a transfer unit 5A to retransfer the toner images transferred on the intermediate transfer element 70 of the intermediate transfer unit 7 from the photosensitive bodies lY, 1M, 1C, and 1K, onto a sheet of printing paper, and a fusing unit 24 to fuse and fix the toner images transferred onto the sheet of printing paper with heat and pressure.
Each of the image forming units 10Y, 10M, 10C and 10K are provided with photosensitive body assemblies 11Y, 11M, 11C and 11K (FIG. 5) having photosensitive bodies 1Y, 1M, 1C and 1K, charging units 2Y, 2M, 2C and 2K and cleaning units 6Y, 6M, 6C and 6K, laser scanning units 3Y, 3M, 3C and 3K (see FIG. 2), and developing units 4Y, 4M, 4C and 4K, which are formed in the proximity of the circumferences of the photosensitive bodies 1Y, 1M, 1C and 1K.
The intermediate transfer unit 7 has primary transfer parts 5Y, 5M, 5C, and 5K pressing the photosensitive bodies 1Y, 1M, 1C, 1K at a predetermined pressure with the intermediate transfer element 70 interposed therebetween.
As shown in FIGS. 1–4, the mounting frame 8 is formed of a casing 81 constructed to be guided and projected forward along left and right supporting rails 82L and 82R of main body 1A, to install the image forming units 10Y, 10M, 10C and 10K and the intermediate transfer unit 7 into the main body 1A.
The casing 81 is provided with an upper cover member 83 to cover an upper portion of the photosensitive body assembly 11Y, and a lower cover member 84 to protect the intermediate transfer element 70 in mounting and dismounting of the intermediate transfer unit 7, and preferably to act as an upper guide of a paper conveying path (at the same time).
Vertical grooves 86 and horizontal grooves 85 are formed at inner surfaces of front and rear walls of the casing 81 to guide positioning pins 75 (FIG. 3) formed at both sides of the intermediate transfer unit 7 to install the intermediate transfer unit 7.
The casing 81 is provided with supports 87Y, 87M, 87C and 87K (FIG. 5) to support the photosensitive body assemblies 11Y, 11M, 11C and 11K including the photosensitive bodies 1Y, 1M, 1C and 1K, the charging units 2Y, 2M, 2C and 2K and the cleaning units 6Y, 6M, 6C and 6K in corresponding assembling positions, respectively. Supporting sliders 88Y, 88M, 88C and 88K (FIG. 3) receive and support the developing units 4Y, 4M, 4C and 4K in corresponding assembling positions, respectively.
Accordingly, in disassembling of the intermediate transfer unit 7 and the image forming units 10Y, 10M, 10C and 10K for maintenance and repair, the mounting frame 8 is guided and projected forward along the left and the right supporting rails 82L and 82R in the main body 1A, as shown in FIG. 1.
Subsequently, the intermediate transfer unit 7 is moved away from the photosensitive body assemblies and then lifted upwardly, as shown in FIG. 5. Durign the lifting procedure, the positioning pins 75 of the intermediate transfer unit 7 are guided along the horizontal grooves 85 and then vertically along the vertical grooves 86, so that the intermediate transfer unit 7 can be easily pulled out.
After pulling out the intermediate transfer unit 7, the photosensitive body assemblies 11Y, 11M, 11C and 11K and the developing units 4Y, 4M, 4C and 4K are moved and then pulled out in the directions shown by the arrows in FIG. 5 from the supports 87Y, 87M, 87C and 87K and the supporting sliders 88Y, 88M, 88C and 88K, respectively.
The procedure for assembling the intermediate transfer unit 7 and the image forming units 10Y, 10M, 10C and 10K into the mounting frame 8 is performed in the opposite order of disassembling them as described above.
The conventional tandem color image forming device 1 as described above has a mounting frame 8 that can easily assemble and disassemble the intermediate transfer unit 7 and the image forming units 10Y, 10M, 10C and 10K. To accurately mount the photosensitive body assemblies 11Y, 11M, 11C and 11K, however, and the developing units 4Y, 4M, 4C and 4K of the image forming units 10Y, 10M, 10C and 10K in position in the mounting frame 8, they should be fabricated to have dimensions that accurately coincide with those of the supports 87Y, 87M, 87C and 87K and the supporting sliders 88Y, 88M, 88C and 88K of the mounting frame 8, respectively.
Fabricating the dimensions in both side components to accurately coincide with one another as described above can complicate the design of the fabricating mold, and can induce assembling errors when assembling both of the side components.
Furthermore, in the conventional tandem color image forming device 1, the photosensitive body assemblies 11Y, 11M, 11C and 11K and the developing units 4Y, 4M, 4C and 4K should be exactly and individually mounted on assembling positions in the mounting frame 8. This is difficult to achieve, and causes assembling efficiency to decrease and increases assembling time, thereby lowering manufacturing productivity.